hi , im jcheesee and nautilus its my main, this build was made from the experience i have had with this champ so I recomend to follow it.

Pros
if played properly he can be a very good supp and tank for the late game
easy spam from the E
with your q well aimed you with the help of the adc can kill a enemy instantly
a good combo can deal the enemy adc a lot of damage and let your´s a easy kill
Cons
can be easily ganked
if the build isnt well done , mana will be a problem
not too much damage
invisibility cancels his ult

I recomend you to main your e and then the q but if you and your adc are diying and losing farm main as well as your e the w wich would give you a shield in case the enemy focuses on you. other think to remember is that if you are aiming a enemy with your q , try using it when he is close to a wal because if you fail, the anchor would shock with the wall and you would be pulled to it, then use your e for the slowdown and activate your shield ( remember that for this type of movement you would need help of your adc)

nautilus is very usefull as a tank because of his w, in case he is about to die, activate in and in case the enemy is chasing you and your alies arent close , use your ulti ( but make it worth) and escape to base.Other way to scape is with your e because of its slowdown.

please remember that this was my first guide, if it were usefull vote it